Known systems for the surface treatment of pieces such as metal pieces comprise a series of tanks containing baths, for example, electrolytic or chemical baths, arranged in succession in a manner such that the pieces coming out of one bath are immersed in the next bath. For processes for cleaning pieces, baths, for example, degreasing baths, washing baths, pickling baths, etc., are arranged in succession.
Surface-treatment plants having the features outlined above are known from U.S. Pat. No. 1,368,357 and U.S. Pat. No. 1,819,603.
For electroplating processes, nickel-plating baths, galvanizing baths, or baths for similar processes for the surface application of metallic coatings are provided in addition to cleaning baths.
In order to immerse the pieces to be treated in the series of baths provided for the treatment, the pieces are first placed in containers which are then moved from one tank to another by means of overhead transfer devices which immerse the containers in the various baths and remove them therefrom according to the predetermined cycles of the process.
However, known transfer devices have the disadvantage of requiring a large amount of space since the containers can be moved by the overhead devices from one tank to another only if the tanks are arranged adjacent one another, generally at a single level or in a single working plane. Moreover, the insertion of the pieces to be treated in the containers and their removal therefrom upon completion of the treatment take place manually so that operators are required for these operations.
The success of the treatment on these pieces may be compromised by vigorous rolling of the pieces to be treated by the structure of the containers.